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    <title>
      Accessibility Object Model, Phase 4
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    <section id="abstract">
      <p class="warning">
        This spec has been deprecated,
        please see the
        <a href="https://github.com/WICG/aom/blob/master/explainer.md">Accessibility Object Model Explainer</a>
        and
        <a href="index.html">index to specs</a>
        for up to date information.
      </p>
    </section>
    <section id="introduction">
      <h1>Introduction</h1>
      <p>
        This document is the spec for Phase 4 of the Accessibility Object
        Model spec. For background, please refer to the
        <a href="https://github.com/WICG/aom/blob/master/explainer.md">
          Accessibility Object Model Explainer</a> for the background and
        motivation, and then
        <a href="index.html">Phase 1</a>,
        <a href="phase2.html">Phase 2</a>, and
        <a href="phase3.html">Phase 3</a>.
      </p>
    </section>
    <section id="computedtree">
      <h2>
        Phase 4: Computed Accessibility Tree
      </h2>
      <p>
        The Computed Accessibility Tree API will allow authors to
        access the full computed accessibility tree - all computed
        properties for the accessibility node associated with each
        DOM node, plus the ability to walk the computed tree
        structure including virtual nodes.
      </p>
      <p>
        This will make it possible to:
      </p>
      <ul>
        <li>write any programmatic test which asserts anything about the semantic properties of an element or a page.
        <li>build a reliable browser-based assistive technology - for example, a browser extension which uses the accessibility tree to implement a screen reader, screen magnifier, or other assistive functionality; or an in-page tool.
        <li>detect whether an accessibility property has been successfully applied (via ARIA or otherwise) to an element - for example, to detect whether a browser has implemented a particular version of ARIA.
        <li>do any kind of console-based debugging/checking of accessibility tree issues.
          react to accessibility tree state, for example, detecting the exposed role of an element and modifying the accessible help text to suit.
      </ul>
      <p>
        One implication of implementing this phase is that all browsers must agree on
        exposing the *same* accessibility tree for the same given webpage, otherwise
        differences will invariably lead to authored pages that work in some browsers
        but not others. Care must be taken to define this phase in such a way that
        maintains a high degree of compatibility between browsers, without exposing any
        internal details and nuances.
      </p>
    </section>
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